Niemann-Pick disease is a progressively debilitating, neurogenetic disorder which is characterized biochemically by the accumulation of sphingomyelin in several tissues and organs in conjunction with deficiency of the lysosomal hydrolase, sphingomyelinase. Detailed description of various phenotypes in terms of cellular pathochemistry and molecular genetics has not been accomplished to date. A major obstacle in this area has been the absence of reproducible techniques for the isolation of homogeneous preparations of sphingomyelinase. Employing novel detergent and chromography systems, we have purified sphingomyelinase to homogeneity. The purified enzyme migrates with an apparent molecular weight of 67,000 daltons is SDS-polyacrylamide gels under both reducing and nonreducing conditions. Kinetic analyses and determinations of the primary protein structure and carbohydrate composition are in progress. Polyclonal antibodies have been raised to the purified enzyme that will assist in cloning the gene for sphingomyelinase. Characterization of the phenotypes of Niemann-Pick disease in terms of protein polymorphisms and specific mutations at the DNA level will be undertaken.